Crosstalk, the unwanted transmission of signals between communication channels, in the context of hearing testing means that an unwanted audible signal is present on the inactive channel. ANSI/ASA S3.6-2010 regulates the maximum allowable levels of crosstalk for a compliant audiometer. Crosstalk occurs when power leaks from one channel to the other in systems where channels are not fully isolated (see FIG. 1).
While purpose-built audiometers meet this standard through the use of hardware designed to electrically isolate the left and right channels, a software audiometer running on a computer or mobile device needs to take extra steps in order to meet the standard. A common approach is to augment the computer or mobile device with external hardware, usually called a DAC, that is custom-designed to generate sound in accordance with the ANSI standard.
In our invention disclosed in International patent application no. PCT/CA2016/000249 filed Oct. 6, 2016, however, we disclosed a novel method of implementing a crosstalk-compensation system entirely through the use of novel software.
In particular, we disclosed a novel computer-implemented method for reducing undesired crosstalk signals on an inactive channel of a device. That method is effective but fairly complex and can involve steps including: (a) determining system volume levels and associated signal amplitudes required to achieve a range of desired audio output attenuation levels on an active channel of the device by (i) measuring an output level at each system volume level of the device from maximum level to minimum level when the associated signal amplitude is set at 1; (ii) converting the output level at each such system volume level into decibels of attenuation; (iii) storing the decibels of attenuation for each system volume level in a database; (iv) querying the database to find the system volume level that attenuates the output level to as close to, but not more than, the desired audio output attenuation level; (v) calculating an attenuation required on the signal amplitude, which when added to the decibel of attenuation achieved at the system volume level, will result in producing the desired audio output attenuation level; (vi) storing the calculated attenuation required on the signal amplitude in the database; and (vii) repeating steps (iv) to (vi) for all system volume levels in the database; (b) determining a crosstalk compensation signal comprising a signal amplitude and associated phase shift required to reduce undesired crosstalk on the inactive channel of the device for each desired audio output attention level in the range of desired audio output attenuation levels by (viii) generating a tone for the desired audio output attenuation level by controlling the system volume level and associated signal amplitude required to generate the tone; (ix) measuring the undesired crosstalk on the inactive channel of the device; (x) calculating a signal amplitude that would be required to eliminate the undesired crosstalk on the inactive channel without modifying the system volume level; (xi) generating a candidate crosstalk compensation signal at a phase of 180 degrees in accordance with step (x); (xii) re-measuring the undesired crosstalk and iteratively adjusting the associated signal amplitude until the measured undesired crosstalk is minimized; (xiii) generating a candidate crosstalk compensation signal at a phase of 0 degrees in accordance with step (x); (xiv) re-measuring the undesired crosstalk and iteratively adjusting the associated signal amplitude until the measured crosstalk is minimized; and (xv) comparing the candidate crosstalk compensation signal at a phase of 180 degrees to the candidate crosstalk compensation signal at a phase of 0 degrees to determine which compensation signal is more effective at reducing the undesired crosstalk, and storing the signal amplitude and phase of the more effective crosstalk cancellation signal in a database; and (c) generating a desired audio output attenuation level on the active channel of the device by querying the database for the system volume level and associated signal amplitude and generating a signal at the determined system volume level and associated signal amplitude required to achieve the desired audio output attenuation level, and generating a contemporaneous crosstalk compensation signal on the inactive channel of the device by querying the database for the signal amplitude and phase and generating a signal at the determined signal amplitude and associated phase shift required to reduce the undesired crosstalk on the inactive channel.
In the present invention, we describe a new and less complex method of implementing a crosstalk-compensation system entirely through the use of novel software that allows for the use of audio hardware that does not fully isolate the left and right channels. In addition, through the teachings of the present invention, it is also possible to build equivalent external hardware that is designed to remove crosstalk from an audio system using the same basic novel technique as described herein.